Doctoral Degrees (Entomology)

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Aspects of the morphology and bionomics of Batrachomorphus cedaranus (Naude) and Lygidolon laevigatum Reut. on black wattle (Acacia mearnsii De Wild)
(1970) Connell, Allan Donovan.; Oosthuizen, Marguerite Poland.; Hepburn, G. A.
No abstract available.
Bionomics and control of the sugarcane insect Numicia viridis Muir (Homoptera: Tropiduchidae)
(1973) Carnegie, Alastair John Michael.; Bosman, Theodore.
Numicia viridis Muir (Homoptera : Tropiduchidae) is an indigenous southern African insect which was 'described in 1931 from specimens collected in Pondoland and Natal. In 1962 it became of economic importance when it was associated with damage caused to sugarcane in both Swaziland and South Africa. Affected cane turned yellow, its leaves dried off prematurely, and an abnormally large amount of trash was produced. was affected. Growth was retarded, and in extreme cases stem texture Since 1962 the insect's association with both sugarcane and alternate host plants has been investigated, and its economic importance assessed. Insectary investigations included studies of life history, developmental stages and behaviour of N. viridis and of its parasites. Two Mirid egg predators (Tytthus mundulus(Breddin)and T. parviceps (Reuter) ) were introduced from Mauritius, but neither became successfully established. Field studies included general ecology, population dynamics, movement, distribution and the development of infestations. The association of N. viridis with 12 sugarcane varieties and with grass communities formed the subject of seven field experiments. All locally grown cane varieties and most grass species could serve as host plants, but differences in egg mortality rates for different host plants were noted. Natural controlling factors were recognised, including biological agents. Of these, two useful egg parasites (Ootetrastichus ?beatus Perkins (Eulophidae) and Oligosita sp. nov. (Trichogrammatidae) were the most important. Attention was given also to chemical control, and it was found that of ten insecticides tested in large scale field experiments, dust and low volume formulations of endosulfan and mercaptothion gave very satisfactory control.
An ecological investigation of the insects associated with exposed carcasses in the Northern Kruger National Park : a study of populations and communities.
(1984) Braack, Lawrence Edward Oliver.; Miller, Raymond Martin.
Extensive seasonal collections along with absolute counts of all the arthropods attracted to medium- and large mammal carcasses resulted in the most complete record of carrion-fauna in Africa to date. The abundance of these species and their seasonal, successional, and diel patterns of carcass-attendance are discussed. More than 98% of species were insects and their presence at the carcass habitat could be classified as obligate, opportunistic, or incidental. A recognisable community of carrion-associated arthropods consistently attracted to the carcass habitat is described, comprising sarcophages, coprophages, keratophages, detritivores, predators and parasites. The interactions and functional ecology of these arthropods is described. The blow-flies Chrysomyia albiceps (Wd.) and C. marginalis (Wd.) were found to be pivotal or key species due to the impact of their larvae on carcass decomposition and their influence on other members of the community. In view of the importance of these blow-flies, their abundance, and the potential role of the adults as dispersal agents of disease organisms, studies were performed to clarify the population dynamics of the two species. The biology and ecology of the immature stages is discussed, including such aspects as the availability of mammal carcasses for oviposition and larval development, and mortality of larvae in the digestive tracts of vultures. By feeding a radioactive isotope of phosphorous (p[32]) to a reared population of adult flies, the dispersal and flight ranges, habitat preferences and population densities of both blow-fly species were studied. The seasonal abundance of C albiceps, C. marginalis, and Lucilia spp. was monitored by monthly trapping at three sites in the study area. Further studies using radioactively-marked blood in a carcass under natural conditions revealed that the distribution of flyspecks deposited by blow-flies is largely dependent upon vegetational structure in the immediate vicinity of the carcass, and the majority of such droplets occurred near the carcass between one and three metres above ground. A distinction in fly-specks was made between vomit droplets, faecal droplets, and the newly tenned discard droplets. The feeding behaviour of C. albiceps and C. marginalis is discussed with reference to the transmission of anthrax in the northern K.N.P.
Ecological correlates : endophagous insects and plants in fynbos.
(1995) Wright, Mark G.; Samways, Michael John.
The objective of this study was to investigate endophagous insect species richness in Fynbos. The influences of plants as determinants of insect occurrence were given special attention. The endophagous insects associated with Proteaceae in Fynbos were compared to endophage assemblages from northern, non-Capensis Proteaceae. The Cape Fynbos genus Protea is utilized by many more insect taxa than the non-Fynbos species. The high diversity of host plants in Fynbos appears to have contributed to generating high, local endophagous insect diversity. Influences of regional climate, biotope and host-plant characteristics on the frequency of occurrence of insect borers exploiting Protea species was investigated in Fynbos. Distinct differences in frequency of encounter of the various insect taxa were recorded for the various host-plants studied. This variability was primarily accounted for by physical host-plant characteristics (infructescence and seed-set variables). These findings have important implications for evolution of insects associated with these plants, as well as for the conservation of insects and in pest control programmes on indigenous cut flowers. The relative species richness of endophagous and ectophagous insects in Fynbos was compared. Gall-forming insects (Diptera: Cecidomyiidae), were found to be considerably more speciose than other feeding guilds, showing that the ratio of endophages to ectophages in sclerophyllous vegetation types is high. The intimate relationship that endophagous insects have with their host plants tends to habitat specialization. These insects are therefore likely to undergo radiation together with their host-plants. Species richness of gall-insects in Fynbos was investigated to establish whether insect richness was proportional to plant species richness. The relationship between gall-insect species richness and plant-species richness was investigated. Fynbos harboured more gall-insect species than other Cape Floristic Region vegetation types. Gall-insect species richness was positively correlated with plant-species richness. Plant species richness appears to have contributed to the evolution of a rich gall-insect fauna in the region. Fynbos gall-insect species richness is comparable to other sclerophyllous vegetation types globally, underscoring the importance of this vegetation type as a centre of galler diversification. Finally, the importance of plant species richness as a determinant of gall-insect species richness was investigated by comparing different sclerophyllous vegetation types under the same climatic conditions. Gall were sampled from Fynbos and Karoo vegetation. Fynbos had higher gall-insect species richness, correlated with plant-species richness. Plant-species richness, or the distal factors that generated it, appear to have contributed significantly to the radiation of gall-insects in this region.
Impact of insect growth regulators on non-target species, with an emphasis on Coccinellids on citrus, in Swaziland.
(1998) Magagula, Cebisile N. N.; Samways, Michael John.
This study investigated effects of insect growth regulators (IGRs), recommended for use on citrus in southern Africa, on non-target organisms, particularly species of Coccinellidae in and around three citrus estates in the lowveld region of Swaziland, i.e. Tambuti, Tambankulu and Tunzini estates. Some of the species are important predators of citrus pest insects. The distribution of coccinellids within an agricultural land mosaic and factors affecting this distribution pattern were also investigated. Results showed that coccinellid densities and species diversity were lowest in the natural veld surrounding the orchards. In contrast, citrus orchards had the highest coccinellid densities and diversity. River borders, along the Great Usuthu river, had intermediate densities and diversity. While temperature, relative humidity and ground insolation had no significant effect on coccinellid population densities, the presence / absence of prey (host plant), on the other hand, was an important factor. This was the case both for phytophagous and predatory coccinellid species. These showed close patterns of distribution with their respective host plants or prey species. Economically important species, such as Rodolia spp., were restricted to the orchards, while other species, especially those whose economic role is uncertain, such as Cheilomenes lunata and Scymnus spp., were found in most habitat types. Coccinellid population densities were assessed during four treatment programmes: 1) an integrated pest management (IPM) programme where no IGRs were used, 2) a programme where any of the recommended IGRs were to be applied, 3) conventional pesticide programme, and 4) an orchard which did not receive any chemically treatment over the last four years (at Tambankulu estate only). Significant differences between treatment programmes were observed at all three estates, when only economically important coccinellid species were assessed. Orchards under an IPM programme (with no IGRs) were found to have significantly higher population densities compared to those in IGR-treated or under a conventional pesticide regime. The untreated orchard at Tambankulu, however, had significantly higher coccinellid densities of economically important species and higher overall population densities than any of the managed orchards. Of the three estates assessed, Tunzini had significantly higher population densities of all beneficial coccinellids, (excluding the untreated orchard at Tambankulu). Natural vegetation around Tunzini and Tambuti contributed to the higher coccinellid densities compared to Tambankulu, which was surrounded by other agricultural land. Laboratory and field experiments on two non-target species, the ladybird Chilocorus nigritus (Fabricius) (all stages) and the moth Bombyx mori (Linnaeus) (larval stage) assessed specific IGR effects, if any. Three IGRs, buprofezin, teflubenzuron (both chitin synthesis inhibitors) and pyriproxyfen (a juvenile hormone analogue) were used. All three pesticides are currently recommended for use on citrus in southern Africa and were tested at the recommended dosages. Laboratory experiments showed that all three IGRs have a negative impact on both non-target species. When B. mori received direct applications, there was larval mortality as a result of the failing to complete moulting or dying immediately after moulting. In addition, no larvae were able to pupate after having fed on contaminated leaves. In the case of C. nigritus, larvae fed IGR-treated scale or sprayed with buprofezin suffered significantly higher mortality than controls, while IGR effects on those sprayed with, or fed scale-treated with, pyriproxyfen or teflubenzuron were not significant. No adults however, emerged from any pupae in any of the treatment groups. All three IGRs had ovicidal activity on C.nigritus eggs. Adult fecundity in both field and laboratory experiments was not affected significantly after exposure to any of the three IGRs. In field experiments, the proportion of larvae of the moth and ladybird that developed up to the reproductive adult stage, after exposure to buprofezin, was not significantly different from the control. This was not the case for pyriproxyfen and teflubenzuron. Buprofezin was therefore found to be the least detrimental of the three IGRs tested. Minimal drift was observed when a knapsack sprayer was used. However, there was spray drift up to 32m (the furthest distance assessed here) where commercial sprayers were used. This suggests that pesticide drift from orchards to adjacent areas would have serious implications for biological diversity in the river borders and rivers adjacent to the estates. The sensitivity of the non-target species to the IGRs tested needs serious consideration, as it indicates a broader spectrum of activity for the compounds than what is promoted. Additionally, natural control may be affected. This is because the timing of IGR applications and increasing coccinellid populations coincide, resulting in a reduced pool of coccinellid predators. This study emphasised the importance of an appropriately heterogenous landscape to maximise habitat availability for the coccinellids. Although the economic role of the multihabitat coccinellid species recorded here is unknown, they nevertheless clearly contribute to citrus pest control. Such a mosaic landscape, in conjunction with IPM, with no IGR use, promotes ecological diversity and controls pests with minimum disruption to biodiversity. The use of IGRs in citrus thus needs carefiil reconsideration in light of the non-target effects observed on the two species, especially the valuable predatory species, C. nigritus.
Response of carabid and cicindelid beetles to various types of landscape disturbances.
(1998) Jaganyi, Joan Nyangasi Ukiru.; Samways, Michael John.
A study of carabids and cicindelids was carried out in eastern South Africa using the same methodology as has been used in the northern hemisphere to obtain a southern hemisphere perspective. The study used the macroecology approach to compare patterns and responses of these animals to anthropogenic disturbances in visually similar habitats (forests, grasslands). Although this is essentially a local component of a larger macroecological study, it is shown that even though species and identities differ between the north and southern hemispheres, the general patterns of community response to anthropogenic disturbances are surprisingly similar. Changes in carabid assemblages were assessed across eight sites or landscape elements experiencing a range of disturbance types, both regular and irregular (such as mowing, fire, irrigation, fertilizers, pesticides, forestry). Direct comparisons were made with similar studies in the Palaearctic. Species diversity, seasonal population variations, population phenology, spatial patterns and mean body size of species assemblages relative to the landscape elements are described. As in the north, intensively disturbed biotopes were impoverished, and natural patches of moist forest acted as habitat sources for these disturbed sinks. Roadside verges were species-rich analogues of natural habitats. The mean body size of carabid assemblages in forest and grassland sites decreased with increasing intensity of disturbance. One contrary comparison with the north was that a plantation, in this case macadamia, was exceptionally rich in carabid species and individuals. Classification and ordination methods identified and characterised the eight sites to six ecological meaningful biotopes for carabids and cicindelids. This also allowed inferences as to how the various landscape disturbances in natural forests, planted pine forests, macadamia plantation, recreational park, road verge grasslands and hayfields affect carabid and cicindelid species richness and abundance. Species assemblages that responded to these anthropogenic impacts were potential indicator groups that can assist in the planning and management of forest and grassland landscapes for conservation of biodiversity. Some management recommendations for these landscapes are given. Individual species-environment relations were investigated using both univariate and multivariate analyses. The solutions to these analyses were then used to describe how species are distributed along major environmental gradients. It was shown that soil characteristics (pH, moisture, twig and/or leaf litter) determine carabid and cicindelid assemblages. Land-use and management regimes influence these patterns. The effect of altitude is masked by the presence of soil characteristics in a multivariate analysis, and more so in the presence of pH and moist soil-sand gradients with changing altitude. In the absence of soil characteristics and in univariate analysis, altitude becomes very important. Altitude has therefore an indirect effect in that it determines climate, which, in turn, determines soil and vegetation type which then determines species presence and abundance. It is concluded that the macroecological approach has great potential for teasing apart local effects from global ones, and can contribute to the conservation of biodiversity at both small and large scales.
Systematic revision of Tricholabiodes Radoszkowski (Hymenoptera: Mutillidae)
(1998) Bayliss, Paul Spencer.; Brothers, Denis John.
This study comprises an examination of over 4000 male specimens, including nearly all type material, a detailed study of the genitalia, and a key to the majority of the species of Tricholabiodes Radoszkowski. Thirty species and subspecies are redescribed and 22 new species described. The 22 newly described species are: T. acer, T. alveolus, T. brothersi, T. concavus, T. convexus, T. denticidatus, T. disgregus, T. femoralis, T. ferrugineus, T. indistinctus, T. inornatus, T. longicarinatus, T. liiridus, T. parallel™, T. paulocellatiis, T. petiolatus, T. protitberans, T. recurvatus, T. sinuatus, T. thisboides, T. tortilis and T. trochantalis. Tricholabiodes semisthataeformis Bischoff and T. pathzii Invrea are synonyms of T. stigmaticus Bischoff and T. pallidicornis Bischoff, respectively. Phenograms and principal component plots were derived to clarify species status, make decisions on species limits and used to determine the morphological similarity between the species. The phenetic analysis was used only as a tool, and not a final product. For the determination of species limits, which included an analysis of 447 specimens, the continuous quantitative and coded characters were analysed separately. Forty-three continuous quantitative characters were analysed either as standardized measurements (against mesosoma length) or as ratios (32), since it was not possible, even via gap coding, to code these characters. Scatterplots and a phenogram from the principal components and cluster analyses respectively, are presented. Size and shape were not particularly helpful characters in determining species limits. One hundred and twenty five coded characters were analysed in a cluster analysis and part of the final phenogram is presented. For the determination of morphological similarity between the species, a hypothetical specimen, typical of each species, was derived. Again, one hundred and twenty-five coded characters were analysed in a cluster analysis and the final phenogram is presented. Representatives from each of the species and subspecies were examined with respect to 93 coded characters. The character states were polarised using the outgroup Dasylabroides Andre. Where Tricholabiodes had all states occurring in Dasylabroides, and the primitive state could not be identified, these characters, and their states, were considered for the entire tribe, and the sister tribe of Dasylabrini, Sphaeropthalmini, was taken as the outgroup. The cladograms were constructed with the software Hennig86. The most variable characters were eliminated from the analysis. Selection of the cladogram representing the most likely phylogeny of the genus was based on parsimony, resolution of the tree, character placement on the tree, comparison of the tree with weighted/unweighted consensus trees and biogeography. The phylogeny presented, which is to be regarded only as a hypothesis, suggests that Tricholabiodes underwent nine separate radiations. The southern African species are divided into two lineages: the first divergence stems from the base of the tree while the more recent lineage stems from the apex. Evidence suggests that the genus arose in central Africa, spreading south (twice) into southern Africa, north into North Africa, west across central North Africa and east into southeastern Asia. The study has also shown that the majority of the species are restricted in their distribution, with none of Palaearctic species occurring in southern Africa, and vice versa. It is hypothesised that the present distribution of the genus is partially restricted by dispersal ability and climate.
Fungal parasitism of cereal aphids in South Africa.
(2002) Hatting, Justin Louis.; Miller, Raymond Martin.; Wraight, Stephen.; Poprawski, Tadeusz.
The Russian wheat aphid, Diuraphis noxia is one of the most destructive exotic invaders of South Africa, capable of reducing individual wheat plant yields by up to 90%. Entomopathogenic fungi are important natural mortality factors associated with this aphid in its Eurasian endemic habitats as well as in the United States and Canada; their impact often exceeding that of predators and parasitoids. The principal objectives of this study included (1) baseline characterization of the aphid-pathogenic flora associated with aphids from South Africa, with special reference to six common cereal aphids, (2) quantification of the comparative impact of the different fungal species on the cereal-aphid complex in three different wheat producing regions of South Africa, (3) field evaluation of the Hyphomycete Beauveria bassiana against D. noxia on resistant wheat, (4) screening of six fungicides for their potential usage in managing entomophthoralean epizootics within greenhouse rearings of the Russian wheat aphid, and (5) development and evaluation of a novel bioassay protocol for screening entomopathogenic Hyphomycetes against D. noxia. A total of nine species of fungi known to infect and kill aphid hosts were collected, including the six entomophthoraleans, Pandora neoaphidis, Conidiobolus thromboides, Conidiobolus obscurus, Entomophthora planchoniana, Conidiobolus coronatus and Neozygites fresenii, and three Hyphomycetes, Beauveria bassiana, Verticillium lecanii, and Paecilomyces farinosus. The former four entomophthoraleans are considered first reports from this country. For the first time, morphological characteristics of these nine South African-collected species are visually depicted and techniques for their isolation and in vitro culture discussed. Seven species of fungi were recorded from D. noxia, of which P. neoaphidis was the most important, causing up to 50% mortality during the late season under dryland conditions in the summer-rainfall region. Mycoses at epizootic levels, together with the large diversity of fungal species recorded from this host, indicated a high level of susceptibility to fungal infection. In contrast, infection of the oat aphid Rhopalosiphum padi remained < 5% despite favourable numbers of hosts and apparently suitable environmental conditions. This phenomenon strongly suggests some level of low susceptibility to fungal infection in this species. Under irrigated conditions m KwaZulu-Natal, the rose-gram aphid Metopolophium dirhodum was the predominant aphid but remained below economical injury levels. Field surveys revealed that this aphid was effectively targeted by P. neoaphidis and C. obscurus, and findings suggest that in some areas of South Africa entomophthoralean fungi effectively suppress this aphid, negating the need for insecticide applications. On average, ca. 61% control of D. noxia on resistant wheat was observed following an application of B. bassiana (5 x 10¹³ conidia per hectare) during the early flag-leaf stage of the wheat. Efficacy of B. bassiana applications on younger plants appeared to be influenced by the level of aphid activity, possibly explained by secondary pick-up of inoculum by D. noxia. These findings accentuate the importance of understanding the tritrophic relationship between host plant, pest and pathogen. The fungicides copper oxychloride, mancozeb + oxadixyl, captab + metalaxyl, bittertanol, iprodione, and mancozeb at a rate of 0.1% active ingredient moderately to strongly inhibited C. thromboides vegetative growth (mean inhibition 81.1 %). Mancozeb at concentrations of 10.0, 2.0, 1.25, 0.5, 0.08, and 0.016% was further evaluated in vitro. The fungus growth cut-off point, midway between 1.25 and 2.0% mancozeb, was calculated and a rate of 1.625% active ingredient per litre of water was used to decontaminate the fungus-infected D. noxia cultures. A novel bioassay protocol was developed, employing live host plants for rearing aphids post inoculation. Using this design against D. noxia, an average LC₅₀ estimate of 85 conidia per mm² for B. bassiana strain GHA was calculated. Control mortality was restricted to levels below 4%. The data indicated high precision due to an average coefficient of variation for slope of less than 20%, and an average chi-squared value of 5.46 ± 2.74 (n = 10 assays). The design will accommodate the use of cereal aphid species other than D. noxia, while live host plants will facilitate tritrophic studies on the effect of host-plant resistance on fungus-induced mortality of D. noxia.
Biology and conservation of the threatened Karkloof blue butterfly Orachrysops ariadne (Butler) (Lepidoptera: Lycaenidae)
(2002) Lu, Sheng-Shan.
The Karkloof blue butt erfly, Orachrysops ariadne (Butler), is endemic to the Mistbelt grassland of KwaZulu-Natal province, South Africa, and is currently Red-listed as 'Vulnerable' . O. ariadne is univoltine and on the wing in March and April, when it utilizes eight species of nectar plants. This study confirmed that the larval hostplant is Indigofera woodii H. Bol. var. laxa H. Bol., an erect variety. It was also confirmed that this butterfly is ant-dependent, with the young larva being taken into the nest of Camponotus natalensis (F. Smith) where development continues, including pupation. This study compares the ecological conditions at the four known locations so as to make informed decision s regarding its conservation. A large proportion of the grassland in KwaZulu-Natal has been aforested and cultivated, and at least 92% of the Mistbelt has been transformed, with only about 1% in good condition remaining. Predictions on the habitat and habit at requirements of this species are necessary for developing a conservation strategy and action plan. Here , we propose O. ariadne as an indicator species for Mistbelt grass land. Saving enough of the remaining Mistbelt grassland is crucial, not just for the survival of the Karkloof blue, O. ariadne, but also for the Mistbelt grassland community as a whole. The population structure and movement of Orachrysops ariadne and O. subravus were studied by mark-release-recapture methods in 1999. There were 290 O. ariadne marked over 48 days between March and April, 124 (42 .8%) were recaptured at least once. Of 631 O. subravus marked over two months between September and November, 311 (49 .3%) were recaptured at least once. Both species exhibited protandry, male appearance about one to two weeks earlier. The sex ratio of O. ariadne is heavily male biased 5.6 :1 (246 males and 44 females), and the sex ratio of O. subravus is 1.6:1 (387 males and 244 females). The Jolly-Seber model was used to estimate daily population numbers (N ᵢ), survival rates (Ø ᵢ), recruitment rates (B ᵢ), proportion of marked animals in the total population (α ᵢ ), and the number of marked animals at risk (M ᵢ) . Average residence times of male adults were generally similar in both species in the range of 5.36-5.44 days, and were slightly longer for male than for female O. subravus (by 4.09 days). 0. ariadne is a strong and rapid back and forth flier, covering mean recapture distances of 157 m, almost twice that of 0. subravus, principally in search of scarce nectar sources. The extreme rarity of 0. ariadne is not so much to do with behaviour, survivorship or longevity, but rather the butterfly is limited in distribution by suitable habitat for both larva and adult. The aim of management is to optimize the habitat so that it best meets the present and future needs of the butterfly. The effects of the current fire regime on the butterfly, host plant and ant host were evaluated here. It is recommended that burning only take place after the larvae have hatch ed and gone underground with the ant host. Using GPS and GIS, core, quality habitat characteristics were defined. In cooperation with the landowner at one site, alien invasive plants are being removed to increase the area of quality habitat. Availability of host plants is limiting for success of the butterfly in the field. Guidelines are provided for propagation and introduction of the host plant, so as to provide the butterfly with more oviposition sites.
Ant management in Western Cape vineyards.
(2004) Addison, Pia.; Samways, Michael John.
No abstract available.
Biotic indicators of grassland condition in KwaZulu-Natal, with management recommendations.
(2005) Kinvig, Richard Grant.; Samways, Michael John.
The South African grassland biome is disappearing rapidly through advancing development and change in agricultural land use. One of the most threatened grassland types, Midlands Mistbelt, in the KwaZulu-Natal Midlands is an extremely diverse and home to many endemic species across an array of taxa. Three taxa, namely, grasses, grasshoppers and butterflies represent various trophic levels, which are important to the functioning of the grasslands. Ten grasslands were sampled by walking ten fifty metre transects for a twelve-month period. The grasslands were selected as they represented a range of management practices and varying environmental conditions. Using Indicator Species Analysis (ISA) twenty-two species of grasshopper were identified as indicators of environmental variables and management practices. The abundances of the various species indicated the intensity of the management regimes or disturbances. Using the twenty-two grasshopper species abundances and a three hundred point sampling assessment of the grasses creates an assessment tool that can rapidly appraise the management of the grassland, but due to lack of data for other taxa, cannot assess whether management practices for the focal taxa create congruent results for non-focal taxa. Two of the three taxa proved to be good indicators of grassland health, whilst the third, butterflies were ineffectual, due to low abundance and richness. From the results it was concluded that burning was taking place to frequently, and required a reduction to every four years, as this would improve butterfly richness and abundance, and increase abundance of endemic and flightless grasshopper speCies. A rotational grazing system needs to be implemented at sites where continual grazing takes place, wildlife or livestock, impacts on the grassland condition and species diversity. Increasing habitat heterogeneity increases species diversity, and allows later successional species to be included in the grasshopper assemblage. Management of the grasslands in the KwaZulu-Natal Midlands needs to be more responsive and adaptive. In addition, small fragment management needs to be intensified to provide a range of habitats and refugia that will suit all species. This study advocates the use of grasshoppers and grasses as suitable biotic indicators of grasslands in the KwaZuluNatal Midlands.
Sugarcane stem borers in Ethiopia : ecology and phylogeography.
(2006) Assefa, Yoseph.; Conlong, Desmond Edward.; Mitchell, Andrew.
Eldana saccharina Walker (Lepidoptera: Pyralidae) is an indigenous insect widely distributed throughout Sub-Saharan Africa that is a major pest of sugarcane in southern Africa. Studies have shown that populations from West Africa have distinct behavioural differences compared to populations from eastern and southern Africa. In addition, the parasitoid guilds attacking populations in these regions are markedly different. This marked behavioural and parasitoid guild variation evoked a hypothesis of genetic diversification. To evaluate this hypothesis a project on the phylogeography of E. saccharina was initiated. The project was planned to include sampling of as many regions as possible in its known range in Africa, to obtain specimens of E. saccharina for genetic analysis. When these surveys were initiated in Ethiopia, it was found that there was no published literature available on the occurrence of stem borers in Ethiopian sugarcane. It was thus clear that no stalk borer/parasitoid surveys had been completed in either sugarcane or any large grass and sedge indigenous hosts in Ethiopia. The study was thus expanded beyond the investigation of only the genetic diversity of E. saccharina, to include area-wide surveys to determine ecological aspects of the borer complex in suspected host plants, including sugarcane, in Ethiopia. In this way the host plant range and distribution of E. saccharina and other sugarcane borers in Ethiopia in particular could be determined, samples for a larger phylogeography project could be collected, and the insect's impact on sugarcane could be assessed. Quantified area-wide surveys of the sugarcane estates and small-scale farmer fields of Ethiopia were conducted between December 2003 and February 2004. The surveys verified the presence of four lepidopteran stem borer species on Ethiopian sugarcane. These were Chilo partellus Swinhoe (Lepidoptera: Crambidae), Sesamia calamistis Hampson (Lepidoptera: Noctuidae), Busseola fusca Fuller (Lepidoptera: Noctuidae) and Busseola phaia Bowden (Lepidoptera: Noctuidae). The surveys indicated that Busseola species are the major and most widely distributed sugarcane stem borers in sugarcane farms of Ethiopia. Over 70% of the peasant sugarcane fields visited were infested by these borers, with the highest levels of infestation (35% and 50%) being in the northern and western part of the country, respectively. Busseola was also the predominant stem borer of sugarcane in two of the three estates (Wonji and Finchawa). Chilo partellus and S.calamistis were recovered in very low numbers at all the commercial estates and from peasant farms in the western part of Ethiopia. However, C. partellus was the predominant sugarcane stem borer in lowland areas of northern, southern and eastern parts of the country. Eldana saccharina was recovered from large sedges in waterways of Metehara and Wonji sugar estates in the central part of the country, and sedges growing around lakes in northern and southern Ethiopia, but not from sugarcane anywhere in Ethiopia. The phylogeographic study conducted on E. saccharina populations from eleven countries of Africa clearly showed the population structure of the insect within the continent. Five hundred and two base pairs of the mitochondrial DNA (mtDNA), corresponding to the Cytochrome Oxidase subunit I (COl) region, were sequenced to clarify phylogenetic relationships between geographically distant populations from eastern, northern, southern and western Africa. Results revealed that E. saccharina is separated into four major populations corresponding to their geographical location, i.e. West African, Rift Valley and two southern African populations. Sequence divergence between the four populations ranged from 1% to 4.98%. The molecular data are congruent with an isolation by distance pattern except for some of the specimens from eastern and southern Africa where geographically close populations are genetically distant from each other. Geographical features such as the Rift Valley and large water bodies in the continent seem to have a considerable impact on the genetic diversity in E. saccharina. Identification of field-collected stem borer specimens was done using classical taxonomic techniques, except for Busseola spp. where DNA barcoding was used. As field-collected larval material of Busseola died before reaching the adult stage, identification of species using adult morphology was not possible. 'Sequence divergence in the COl gene was used as a tool to identify the species of Busseola attacking Ethiopian sugarcane. Partial COl sequences from Ethiopian specimens were compared with sequences of already identified noctuid species from the East African region. Results of the sequence analysis indicated that the Busseola species complex in Ethiopian sugarcane comprised B. fusca and B. phaia. Sequence divergences between Ethiopian Busseola species was as high as 5.0 %, whereas divergences within species were less than 1% in both species identified. Several larval parasitoids, bacterial and fungal diseases of stem boring caterpillars were also recorded in Ethiopian sugarcane. Amongst these was Cotesia flavipes Cameron (Hymenoptera: Braconidae). This exotic parasitoid has been introduced into several African countries for the control of C. partellus in maize and sorghum, but had never been released in Ethiopia. To investigate the origin of C. flavipes in Ethiopian sugarcane, molecular analyses were conducted on Ethiopian specimens from sugarcane and specimens of C. flavipes from different countries of Africa released from the Kenyan laboratory colony, again using COl sequences. Results of the analysis revealed that the C. flavipes population that had established in sugarcane fields of Ethiopia was similar to the south east Asian populations released against C. partellus in maize in other parts of Africa, and different from other populations of this species, providing evidence that the Ethiopian C. flavipes is likely to be a descendant of the original Pakistani population that was released in different parts of Africa. The study reveals the importance of lepidopteran stem borers in sugarcane production in Ethiopia and highlights the role of molecular methods in species identification and determining phylogenetic relationships. More importantly, this study establishes the continental phylogeographical pattern of the indigenous moth, E. saccharina. The impact of geological events, geographic barriers and cropping systems on the evolution, distribution and abundance of stem borers are discussed. Future areas of research for understanding more about the phylogeographic relationships of E. saccharina and management of stem borers are discussed.
Investigations into the incidence and ecology of bilobata subsecivella (zeller) (lepidoptera: gelechidae) : a new pest of groundnut in South Africa.
(2015) Buthelezi, Nokubekezela Makhosi.; Conlong, Desmond Edward.; Olckers, Terence.
The leaf-mining moth, Bilobata subsecivella (Zeller) (Lepidoptera: Gelechiidae), thought to be an invasion from Indo-Asia (where it is known as Aproaerema modicella (Deventer); but hereafter referred to as B. subsecivella) has become a major pest of groundnut (Arachis hypogaea L.) and soya bean (Glycine maxi (L.) Merr.) in South Africa and Africa as a whole. Following the sudden outbreaks of B. subsecivella as a new pest of groundnut in a number of African countries, the continent has been confronted with the problem of having no information on the biology and ecology of the pest that can be used for its management/control. In this context, the main aim of the research for this thesis was to study the biology and ecology of B. subsecivella in South Africa with the main objective of obtaining information that will assist in its management as a novel pest of groundnut. To achieve this objective, several studies were carried out. First, a detection survey of B. subsecivella infestation was conducted on groundnut, soya bean and lucerne (Medicago sativa L.), the common host crops for B. subsecivella in India, at six widely separated sites in South Africa during the 2009/2010 growing season. The sites included the Agricultural Research Council research stations at Potchefstroom and Brits as well as the farms surrounding the Brits research farm in the North West province, Vaalharts Research Station in the Northern Cape province, the Department of Agriculture Lowveld Agricultural Research Station near Nelspruit in Mpumalanga province, and Bhekabantu and Manguzi in the northern part of the KwaZulu-Natal province. The study had three objectives. The first was to build a complete host crop/plant list and record damage symptoms caused by B. subsecivella in South Africa. The second was to identify the pest to species level. The third was to determine its inter- and intra-population genetic diversity by analysing in, both cases, the mitochondrial DNA (mtDNA) COI gene of specimens collected from these sites. Sixty specimens comprising 24 larvae, 24 pupae and 12 moths were collected from the six survey sites, and their mtDNA COI were sequenced and compared with those from the Barcode of Life Data System (BOLD) gene bank. Infestation by B. subsecivella was observed on groundnut and soya bean, but not on lucerne. The mtDNA COI from all specimens of the pest, irrespective of whether they were from groundnut or soya bean, matched 100% with the sequences in BOLD belonging to a B. subsecivella population occurring in Australia (referred to as Aproaerema simplexella (Walker)) and known as the soya bean moth in that country). There was very little genetic diversity between and within the populations from the six sites, which suggested that the populations were maternally of the same origin. Further molecular and phylogenetic studies were also completed to determine the evolutionary relationships between B. subsecivella populations collected from Australia, Africa and India. These studies involved sequencing and analysing five gene regions of mitochondrial and nuclear DNA, including COI, cytochrome oxidase II (COII), cytochrome b (cytb), 28 ribosomal DNA (28S rDNA), and intergenic spacer elongation factor-1 alpha (EF-1 ALPHA). The mtDNA COI analysis also included B. subsecivella (but called A. simplexella) sequences downloaded from the National Center for Biotechnology Information (NCBI) GeneBank collected from different areas in Australia. In four phylogenetic trees (COI, COII, cytb and EF-1 ALPHA), sequences of B. subsecivella personally sampled from Australia were grouped separately from the others, whereas sequences of B. subsecivella from South Africa, India and Mozambique were clustered in one group in most cases. Furthermore, in the mtDNA COI phylogenetic tree, one Australian sequence of B. subsecivella that was downloaded from the NCBI GeneBank was grouped with other sequences from South Africa, India and Mozambique. Moreover, one sequence of B. subsecivella personally sampled from Australia was grouped with the other two sequences of B. subsecivella from Australia that were downloaded from the NCBI GeneBank. Based on these results, it could be hypothesized that there is genetic diversity within B. subsecivella populations in Australia. The mtDNA COI gene analysis in the current study revealed that there are B. subsecivella populations in Australia that are similar to the B. subsecivella populations in South Africa, Mozambique and India. Phylogenetic analysis of the 28S gene region revealed a lack of genetic diversity between sequences of B. subsecivella from India, South Africa, Mozambique and Australia. Genetic pairwise distances between the experimental sequences ranged from 0.97 to 3.60% (COI), 0.19% to 2.32% (COII), 0.25 to 9.77% (cytb) and 0.48 to 6.99% (EF-1 ALPHA). Field experiments were then conducted at Vaalharts, Brits, Nelspruit, Manguzi and Bhekabantu during the 2010/2011 and 2011/2012 growing seasons. These experiments pursued three objectives. The first one was to determine B. subsecivella infestation levels on groundnut, soya bean, lucerne, pigeon pea (Cajanus cajan L.) and lablab bean (Lablab purpureus L.) under field conditions. The second was to develop a host plant list for B. subsecivella and the third was to determine the effect of cypermethrin application on damage by B. subsecivella to groundnut and soya bean plants. In the 2010/2011 season, larval infestation was monitored on groundnut crops planted in November 2010 and January 2011. In the 2011/2012 season, larval infestation was monitored on groundnut, soya bean, lucerne, pigeon pea and lablab bean planted in November 2011 and January 2012. Wild host plants were inspected for damage symptoms and the presence of larvae. An experiment which examined the effect of cypermethrin application on B. subsecivella damage to groundnut and soya bean plants was completed in the 2011/2012 season at Vaalharts and Nelspruit. A survey for wild plant hosts of B. subsecivella was conducted in the proximity of the field experiments during the 2011/2012 growing season, as well as in winter. Amongst the host crops tested, soya bean was highly infested by B. subsecivella followed by groundnut, at all sites. The pest was also observed on pigeon pea at all sites, but the infestation was very low, while lucerne had very low larval infestation. No infestation was observed on lablab bean across these sites. Groundnut and soya bean crops planted in January were severely infested by B. subsecivella, compared to the crops planted in November; however, B. subsecivella infestation on crops was observed 5-6 weeks after crop emergence. Sprays of cypermethrin on groundnut and soya bean reduced larval infestation in both crops to very low levels. Wild plant hosts identified were from five families which included three species in the Leguminosae, two species in the Convolvulaceae, two species in the Malvaceae and one species each in the Lamiaceae and Asteraceae. Seasonal monitoring of the flight activity of B. subsecivella moths was completed at Manguzi, Bhekabantu, Nelspruit, Brits and Vaalharts over a two-year period (from November 2010 to December 2012). The objective of this study was to monitor the flight activity of B. subsecivella in order to understand its dispersal and off-season survival tactics and to predict its initial occurrence. Pheromone traps were used to monitor the moths’ flight activity. Information collected included climatic data (rainfall, temperature and humidity) that were obtained from ARC weather stations placed at four planting sites. Pearson’s test for correlation was performed to assess the relationship between B. subsecivella moth catches and environmental factors (rainfall, temperature and humidity). Results from this study showed variation in B. subsecivella populations throughout the monitoring period. The highest peak in B. subsecivella catches was between January and April/May for both seasons. Though low in numbers, B. subsecivella moths were caught in winter at Manguzi, Nelspruit, Vaalharts and Bhekabantu. No B. subsecivella moths were trapped during the winter months at Brits. Pearson’s test for correlation indicated that there was a significant negative association between temperature and B. subsecivella catches in pheromone traps at Nelspruit, whereas at Vaalharts there was a significant positive association between humidity and B. subsecivella catches. There was no correlation between environmental factors and B. subsecivella catches at Manguzi and Brits. Furthermore, it was found that B. subsecivella in Australia (moths collected for DNA analysis in the current study) responded to the species-specific lure that was developed from the sex pheromone of B. subsecivella, referred to as A. modicella in India. Overall, the study revealed important ecological and genetic information on B. subsecivella populations occurring in southern Africa. More importantly, this study established the genetic connection between B. subsecivella populations from Australia, India and Africa. Hence, the species conforming to these populations were tentatively synonymized as B. subsecivella in this thesis.
Native range studies on insect herbivores associated with fireweed (Senecio madagascariensis) in KwaZulu-Natal, South Africa, with prospects for biological control in invaded countries.
(2017) Egli, Daniella.; Olckers, Terence.; Harvey, Kerinne Jean-Maree.
Senecio madagascariensis Poir. (fireweed; Asteraceae), native to southern Africa and Madagascar, has invaded Australia, Hawaii, South America and Japan, reducing pastoral productivity and poisoning livestock. Interest in biological control by Australia and Hawaii led to initial surveys for potential insect agents in Madagascar. However, molecular evidence revealed that both the Australian and Hawaiian populations originated from KwaZulu-Natal Province, South Africa. Efforts to find suitable biocontrol agents have since been focussed within this region. Studies on potential biocontrol agents in the weed’s native range, which consider its centre of origin, closely related plants and seasonal variation in the abundance of its natural enemies, can provide valuable information for selecting host specific and effective agents. This study aimed to prioritise potential insect agents for Australia and determine their response to possible changes in alkaloid concentrations in plants from within the invaded Australian range. The insect herbivore fauna associated with S. madagascariensis was quantitatively surveyed across 21 sites in KwaZulu-Natal to provide a comprehensive list of herbivores and identify potential agents. A total of 64 herbivorous taxa were recorded. Many of these were recorded rarely, but at least 17 taxa were considered as potential agents having been successful in previous biological control programs. Of these, the most promising were a capitulum feeder (Lepidoptera: Pyralidae), three stem borers (Coleoptera: Curculionidae; Diptera: Tephritidae; Lepidoptera: Tortricidae) and a root-feeding flea beetle (Coleoptera: Chrysomelidae: Alticinae). Biological control programs are more successful when agents attack the target plants throughout the year. The abundance of the insects associated with S. madagascariensis was sampled once per season at two sites in Pietermaritzburg to determine which are present throughout the year and are thus capable of inflicting sustained damage. There was significant seasonal variation in the abundances of the main insect taxa. Of the most promising potential agents, four were recovered all year round, two during three seasons, two during two seasons and one during summer only. Releasing a complement of natural enemies that attack the plant at different times may thus be required to ensure that S. madagascariensis is attacked throughout the year. A number of invasive Asteraceae have been targeted for biological control. An evaluation of the successes and failures of different insect taxa and feeding guilds used in previous programs was carried out to prioritise agents that are most likely to be successful on fireweed. The most effective insect taxa for the biocontrol of species of Asteraceae were Coleoptera (Curculionidae and Chrysomelidae) and Lepidoptera (Pterophoridae and Tortricidae), while root-feeding and stem-feeding species were the most effective guilds. This verified that the root-feeding flea beetle (Chrysomelidae), stem-boring moth (Tortricidae) and stem-boring weevil (Curculionidae) should be prioritized as candidate agents for S. madagascariensis. Agent host specificity is particularly important for Australia which has 87 native Senecio species (Hawaii has none). The field host range of endophagous Coleoptera, Lepidoptera and Diptera associated with fireweed was assessed by comparisons of these taxa across 18 Senecio species native to South Africa. Ten plants of each Senecio species were collected from each of three sites. The COI gene of insect larvae recorded within the tissues of the various Senecio species was sequenced to assess their host specificity. Stem-boring Curculionidae, capitulum-feeding Diptera and stem-boring and capitulum-feeding Lepidoptera that were recorded on S. madagascariensis were restricted to the Senecio madagascariensis species complex, and could thus be suitable for release in Australia and almost certainly in Hawaii. Laboratory host-range tests in Australia are needed to confirm the specificity of these insects. Invasive species have a large adaptive capacity to establish successfully in new environments and may evolve in response to the new range. It is imperative to understand whether any adaptive or evolutionary response can influence a weed’s interaction with natural enemies from the native range. In particular, increased alkaloid concentrations in Australian fireweed populations may affect the efficacy of insect biocontrol agents. A field experiment compared the biomass, insect assemblages recruited in the field, and alkaloid profiles between invasive Australian and native South African populations of S. madagascariensis. Minimal variation in plant biomass and insect community composition was detected, despite some variation in alkaloid composition and concentrations, between the regions and countries. There was no relationship between alkaloid concentrations and insect communities indicating that potential insect biocontrol agents are unlikely to be affected by increased plant defences in Australian fireweed populations. Several insect agents were prioritised for further consideration in Australia based on the different criteria examined in this thesis. The root-feeding flea beetle (Longitarsus basutoensis Bechnyé), stem-boring weevil (probably Gasteroclisus tricostalis (Thunberg)) and stem-boring tortricid moth (unidentified species) will be the focus of additional field and laboratory studies that examine their life cycles and host range, prior to their introduction into quarantine in Australia.
Understanding the fitness, preference and performance of specialist herbivores of the Southern African biotype of Chromolaena Odorata (Asteraceae), and impacts on phytochemistry and growth rate of the plant.
(2019) Dube, Nontembeko.; Munyai, Thinandavha Caswell.; Zachariades, Costas.; Uyi, Osariyekemwen.
The invasiveness and negative impacts of the alien shrub, Chromolaena odorata (L.) (Asteraceae) in South Africa resulted in the initiation of a biological control programme against the weed in the late 1980s. After the release of seven biocontrol agents, only two have successfully established to date viz. a leaf mining fly, Calycomyza eupatorivora Spencer (Diptera: Agromyzidae) and a moth with defoliating larvae, Pareuchaetes insulata Walker (Lepidoptera: Erebidae: Arctiinae). Surveys conducted suggested that C. odorata densities seem to be low in KwaZulu-Natal (KZN) province where P. insulata is present whilst its infestation is increasing in other places such as Limpopo province where the moth is absent. This study aimed to examine the life history traits, preference and performance of two biocontrol agents, viz. Dichrorampha odorata (Lepidoptera: Tortricidae) and Polymorphomyia basilica (Diptera: Tephritidae). A further objective of the study was to measure the effects of one of the established agents, P. insulata, on the competitive ability and defence mechanism of C. odorata by indirectly testing the predictions of the Evolution of Increased Competitive Ability (EICA). Studies of life history traits of D. odorata in the laboratory indicated that the moth possesses good biological control attributes such as short-lived adults with high mating success, fecundity and egg hatchability. Of the 34 asteraceous plants subjected to larval no-choice tests, only C. odorata could sustain complete development of D. odorata to adulthood, although there was slight initial boring on 14 test species (plus C. odorata). Adult no-choice tests using seven test-plant species that were damaged in larval no-choice tests were consistent with the earlier trials, with larval damage, pupae and adults of D. odorata recorded from only C. odorata. This demonstrated that only C. odorata is a suitable host for D. odorata in South Africa and permission for the release of this first shoot-tip attacking agent was granted for biocontrol of C. odorata in South Africa. To predict the efficacy of D. odorata as a biological control of C. odorata, a 9-month laboratory study was carried out. Plant growth metrics were compared across three treatments i.e. 0, 50 and 100% where newly hatched D. odorata larvae were inoculated onto the shoot tips of C. odorata. At all treatment levels, the basal stem diameter of C. odorata was not affected by D. odorata larval feeding whilst the height of the main shoot and flower production of C. odorata were reduced at 50 and 100% relative to the control treatment. In general, the impacts of D. odorata on the weed were relatively small even though statistically significant, suggesting that the moth will modestly reduce the height and flower production of C. odorata. Positive biological characteristics of P. basilica include a high rate of increase, long-lived and mobile adults, the ability of females to produce viable offspring without repeated mating, the ability of adults to eclose from galls on dry stems and the production of several generations per year. Thirty-two asteraceous plants were investigated to determine host specificity of P. basilica in single-choice adult tests and using single pairs of adults in no-choice tests, under laboratory conditions. Oviposition and larval development through to adulthood occurred on three other South American and on two South African species; one in the same tribe Eupatorieae, closely related to C. odorata and another one in the Astereae, less closely related to the weed, but both at a lower and slower rate. Females tended to retain their eggs under no-choice conditions in the presence of an unsuitable host, and to compensate by ovipositing at a higher rate when presented later with a C. odorata plant. Overall, this study predicts the ability of P. basilica to stretch to areas where P. insulata has failed to establish and supports the suitability of P. basilica for release in South Africa. To determine the mechanism behind the decrease of C. odorata densities in KZN province, where the specialist herbivore P. insulata is present, compared to Limpopo province, where the weed is increasing and the moth is absent, the Evolution of Increased Competitive Ability (EICA) hypothesis was indirectly tested on plant defence and growth rate metrics. Inconsistent with EICA, total phenolics and tannins were generally higher in Thohoyandou (Limpopo province) (without P. insulata) and Komatipoort (Mpumalanga province) (with P. insulata) and lower in Pietermaritzburg (KZN province) (without P. insulata) and Umkomaas (KZN province) (with P. insulata). Flavonoids varied between the four locations, with higher concentrations in Komatipoort compared to Thohoyandou and Umkomaas, but not different to Pietermaritzburg. Growth parameters such as stem diameter, number of shoots and number of flowering shoots from the garden experiment, supported the prediction of EICA, as plants from the Thohoyandou and Pietermaritzburg sites, where P. insulata is absent, showed stronger growth and reproductive potential. This study demonstrates the possible role of P. insulata in the decrease in population of C. odorata where the moth has persisted and suggests that other biotic and abiotic factors could be responsible for the unpredicted results for phytochemistry assays. The second part of the EICA hypothesis posits that “specialist herbivores will demonstrate improved performance on plant individuals originating from an area where plants have been introduced”. Consistent with EICA, Pareuchaetes insulata immature stages (newly hatched larvae-adult eclosion) that fed on leaves from Umkomaas, had prolonged development compared to larvae that were fed on leaves from Thohoyandou and Pietermaritzburg, and Komatipoort. Larvae and pupae that fed on the leaves from shade from Komatipoort had developmental trends intermediate between larvae feeding on the leaves from the shade from Thohoyandou and Umkomaas. Overall survival was lowest on leaves of plants obtained from Komatipoort. Contrarily, location did not appear to influence pupal mass but this variable was higher in plants in the full sun. In sum, the existing reassociation time may not be enough for evolutionary changes to have occurred in C. odorata defence and P. insulata response to plant evolution, and could explain the inconsistency in some P. insulata performance parameters on infested and uninfested populations of C. odorata. The roles of pyrrolizidine alkaloids (PAs) as plant defences and in P. insulata mating behaviour are well known. The PAs in the roots of the southern African biotype (SAB) of C. odorata were therefore examined. Two PAs, rinderine and its stereoisomer N-oxide intermidine, were isolated from the roots of the SAB of C. odorata using GC-MS. The structures and configuration were confirmed by chemical and spectroscopic methods, especially one- 1H dimensional NMR analysis. Therefore, confirmation of rinderine and intermidine in C. odorata in this study substantiate the establishment and spread of P. insulata in southern Africa due to, among other factors, reduced predation through defence by sequestered PAs. This study demonstrated positive biological characteristics and high preference and performance of both the moth with shoot-tip boring larvae D. odorata and the stem-galling fly P. basilica on C. odorata compared to non-target plants, which highlights positive prospects for the biological control programme of C. odorata in South Africa. This study reports for the first time two pyrrolizidine alkaloids viz. intermidine and rinderine in southern African C. odorata. Aspects of EICA were not straightforward; however, this study showed the contribution of P. insulata to the reduction of C. odorata where the moth is present and further provides direction for future research for the biological control of C. odorata in South Africa.
Pre-release evaluation of the flea beetle Heikertingerella sp. (Coleoptera: Galerucinae: Alticini), a potential biological control agent for the invasive weed Tecoma stans L. (Bignoniaceae) in South Africa.
(2024) Madire, Lulama Gracious.; Olckers, Terence.; Simelane, David Okhi.
The root-feeding beetle Heikertingerella sp. (Coleoptera: Chrysomelidae) was introduced into quarantine in South Africa for evaluation as a biological control agent of the invasive tree Tecoma stans L. (Bignoniaceae). Larval feeding damages the roots, potentially reducing the weed’s growth and reproduction. Pre-release studies in quarantine included several aspects. Studies on the beetle’s biology and host specificity were conducted to confirm its safety for release in South Africa. The impact of varying beetle densities on plant fitness was assessed to determine its likely impact in the field. The effect of local climate on the beetle’s potential to establish throughout the weed’s range in South Africa was predicted using climate-modelling software. The interaction between Heikertingerella sp. and a leaf-feeding agent already established in South Africa was investigated. Finally, the effect of host-plant age and nutrient enhancement on mass-rearing activities was studied, to optimize beetle numbers for releases. The beetle proved host specific resulting in the granting of permission for its release in South Africa. There were significant reductions in plant growth and biomass accumulation in the beetle-exposed plants, relative to the controls, indicating that Heikertingerella sp. is sufficiently damaging. Climate matching revealed that Heikertingerella sp. is likely to perform best at coastal sites in South Africa, with the colder, more inland, areas within the weed’s range proving less suitable. The beetle proved compatible with a defoliating agent established in South Africa, with evidence of positive interactions that are likely to enhance their combined impact on the weed. Trials involving plants of varying age and nutritional enhancement revealed that 3-year-old plants, which were supplemented by either medium or high levels of fertilizer, were best suited for F1 progeny production and therefore for the mass-rearing of Heikertingerella sp. for releases. The results of this study should also benefit other countries in Africa and elsewhere in the world, where the plant is invasive.

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